This invention concerns a receiver system for processing a high definition television signal, e.g., of the VSB-modulated type proposed by the Grand Alliance in the United States.
The recovery of data from modulated signals conveying digital information in symbol form usually requires three functions at a receiver: timing recovery for symbol synchronization, carrier recovery (frequency demodulation to baseband), and channel equalization. Timing recovery is a process by which a receiver clock (timebase) is synchronized to a transmitter clock. This permits a received signal to be sampled at optimum points in time to reduce slicing errors associated with decision-directed processing of received symbol values. Carrier recovery is a process by which a received RF signal, after being frequency down converted to a lower intermediate frequency passband (e.g., near baseband), is frequency shifted to baseband to permit recovery of the modulating baseband information. Adaptive channel equalization is a process by which the effects of changing conditions and disturbances in the signal transmission channel are compensated for. This process typically employs filters that remove amplitude and phase distortions resulting from frequency dependent time variant characteristics of the transmission channel, to provide improved symbol decision capability.
In accordance with the principles of the present invention, a system for processing a received Vestigial Sideband (VSB) modulated signal containing high definition television information includes a digital demodulator responsive to a pilot signal component in the received HDTV signal. The digital demodulator includes a phase control loop with a data downsampling network.